Chemical mechanical polishing/planarization (CMP) is a key process of smoothing surface of semiconductor wafers through both chemical etching and physical abrasion. A semiconductor wafer is mounted onto a polishing head, which rotates during a CMP process. The rotating polishing head presses the semiconductor wafer against a rotating polishing pad. Slurry containing chemical etchants and colloid particles is applied onto the polishing pad. Irregularities on the surface are removed to result in planarization of the semiconductor wafer.
In a CMP process, conditioner disks are used to prepare and maintain the surface of polishing pad. A conditioner disk removes the debris on the polishing pad surface and revives the polish pad surface to ensure a stable CMP process. A conditioner disk generally comprises abrasive particles fixed on a substrate. Non-uniformity of the surface of the conditioner disk can result in non-uniformity in smoothness of the resulting wafer. In addition, some abrasive particles might be dislodged and pulled out from the surface. Such dislodgement and pull-out cause further deterioration of the wafer surface uniformity.
Meanwhile, the size of semiconductor wafers has increased to improve throughput and reduce cost per die. For example, in the transition from 300 mm to 450 mm wafer size, the wafer area increases by 125%. The uniformity in smoothness of the whole wafer becomes more difficult to maintain in the more-than-doubled-sized wafer.